The environment is replete with pests and numerous methods have attempted to control pests infestations of plants. Commercial crops are often the targets of insect attack. Substantial progress has been made in the last few decades towards developing more efficient methods and compositions for controlling insect infestation in plants.
Chemical pesticides have been very effective in eradicating pest infestation. However, there are several disadvantages to using chemical pesticidal agents. Not only are they potentially detrimental to the environment, but they are not selective and are harmful to various crops and non-target fauna. Chemical pesticides persist in the environment and generally are slow to be metabolized, if at all. They accumulate in the food chain, and particularly in the higher predator species where they can act as mutagens and/or carcinogens to cause irreversible and deleterious genetic modifications. There has thus been continued controversy in the use of chemical insecticides to combat crop pests. They can rapidly develop resistance against these insecticides because of repetitive usage of the same insecticide or of insecticides having the same mode of action, and because accumulation also results in the development of resistance to the agents in species higher up the evolutionary ladder.
Control of insect pests on agronomically important crops is important, particularly insect pests which damage plants belonging to the Solanaceae family, especially potato (Solanum tuberosum), but also tomato (Solanum lycopersicum), eggplant (Solanum melongena), capsicums (Solanum capsicum), and nightshade (for example, Solanum aculeastrum, S. bulbocastanum, S. cardiophyllum, S. douglasii, S. dulcamara, S. lanceolatum, S. robustum, and S. triquetrum), particularly the control of coleopteran pests.
Biological control using extract from neem seed has been shown to work against coleopteran pests of vegetables. Commercially available neem-based insecticides have azadirachtin as the primary active ingredient. These insecticides are applicable to a broad spectrum of insects. They act as insect growth regulator; azadirachtin prevents insects from molting by inhibiting production of an insect hormone, ecdysone.
Biological control using protein Cry3A from Bacillus thuringiensis varieties tenebrionis and san diego, and derived insecticidal proteins are alternatives to chemical control. The Bt toxin protein is effective in controlling Colorado potato beetle larvae either as formulations sprayed onto the foliage or expressed in the leaves of potatoes.
An alternative biological agent is dsRNA. Over the last few years, down-regulation of genes (also referred to as “gene silencing”) in multicellular organisms by means of RNA interference or “RNAi” has become a well-established technique.
RNA interference or “RNAi” is a process of sequence-specific down-regulation of gene expression (also referred to as “gene silencing” or “RNA-mediated gene silencing”) initiated by double-stranded RNA (dsRNA) that is complementary in sequence to a region of the target gene to be down-regulated (Fire, A. Trends Genet. Vol. 15, 358-363, 1999; Sharp, P. A. Genes Dev. Vol. 15, 485-490, 2001).
Over the last few years, down-regulation of target genes in multicellular organisms by means of RNA interference (RNAi) has become a well established technique. Reference may be made to International Applications WO 99/32619 (Carnegie Institution) and WO 00/01846 (by Applicant).
DsRNA gene silencing finds application in many different areas, such as for example dsRNA mediated gene silencing in clinical applications (WO2004/001013) and in plants. In plants, dsRNA constructs useful for gene silencing have also been designed to be cleaved and to be processed into short interfering RNAs (siRNAs).
RNAi has also been proposed as a means of protecting plants against plant parasitic nematodes, i.e. by expressing in the plant (e.g. in the entire plant, or in a part, tissue or cell of a plant) one or more nucleotide sequences that form a dsRNA fragment that corresponds to a target gene in the plant parasitic nematode that is essential for its growth, reproduction and/or survival. Reference may be made to the International Application WO 00/01846 (by Applicant) and U.S. Pat. No. 6,506,559 (based on WO 99/32619).
Although the technique of RNAi has been generally known in the art in plants, C. elegans and mammalian cells for some years, to date little is known about the use of RNAi to down-regulate gene expression in insects. Since the filing and publication of the WO 00/01846 and WO 99/32619 applications, only few other applications have been published that relate to the use of RNAi to protect plants against insects. These include the International Applications WO 01/37654 (DNA Plant Technologies), WO 2005/019408 (Bar Ilan University), WO 2005/049841 (CSIRO, Bayer Cropscience), WO 05/047300 (University of Utah Research foundation), and the US application 2003/00150017 (Mesa et al.).
The present invention provides target genes and constructs useful in the RNAi-mediated insect pest control, especially the control of insect plant pathogens. The present invention also provides methods for controlling insect pest infestation by repressing, delaying, or otherwise reducing target gene expression within a particular insect pest.